The invention relates generally to lactacystin and analogues thereof.
Eukaryotic cells contain multiple proteolytic systems, including lysosomal proteases, calpains, ATP-ubiquitin-proteasome dependent pathway, and an ATP-independent nonlysosomal process. The major neutral proteolytic activity in the cytosol and nucleus is the proteasome, a 20S (700 kDa) particle with multiple peptidase activities. The 20S complex is the proteolytic core of a 26S (1500 kDa) complex that degrades or processes ubiquitin-conjugated proteins. Ubquitination marks a protein for hydrolysis by the 26S proteasome complex. Many abnormal or short-lived normal polypeptides are degraded by the ubiquitin-proteasome-dependent pathway. Abnormal peptides include oxidant-damaged proteins (e.g., those having oxidized disulfide bonds), products of premature translational termination (e.g., those having exposed hydrophobic groups which are recognized by the proteasome), and stress-induced denatured or damaged proteins (where stress is induced by, e.g., changes in pH or temperature, or exposure to metals). In addition, some proteins, such as casein, do not required ubquitination to be hydrolyzed by the proteasome.
The proteasome has chymotryptic, tryptic, and peptidyl-glutamyl peptide hydrolizing activities, i.e., the proteasome can cleave peptides on the carboxyl side of hydrophobic, basic, and acidic residues, respectively.